The present invention relates to a license plate assembly comprising a housing having a back plate on which there is arranged a light guide and a semi-transparent and reflective license plate. The light guide is illuminated from one or more of its side faces and the light guide. The license plate is mounted in front of the light guide, typically by means of a frame.
Commonly employed license plates for motor vehicles for use on roads such as cars, busses and trucks and for trailers, typically are illuminated from their front face when it is dark. In particular, the license plates typically have indicia representing the license plate number issued by the appropriate national authorities on a retroreflective background. This retroreflectivity enhances visibility of the plate during day time conditions and also during night time conditions when lights of other motor vehicles or street light impinges upon the front face of the license plate. But in order to meet regulatory requirements, the license plate also needs to be illuminated with lights arranged on the motor vehicles. Thus, typically, lights are arranged aside of the license plate so as to illuminate the front face of the license plate.
Such an arrangement has the disadvantage of limiting the design possibilities of car manufacturers. In particular, the lights that need to be arranged along one or more sides of the license plate prevent the car manufacturer of making more appealing designs as the lights often appear as a disturbing element in the design. Furthermore, such front-lit license plates may suffer from a non-uniform illumination of the license plate. Typically also more powerful light sources may be required to light a license plate from the front, thus resulting in more power consumption.
DE 297 12 954 discloses a license plate arrangement that is illuminated from the back. In particular, this German utility model discloses a stiff transparent plastic plate on which the license plate number is depicted as opaque indicia. The stiff plastic plate is held in front of an electroluminescent foil through a holding frame. The electroluminescent foil when activated illuminates the plastic plate from the back. Such an arrangement has the disadvantage that no retroreflectivity is provided which is a requirement of the regulatory authorities of many countries. A further back-lit license plate is disclosed in U.S. Pat. No. 5,692,327.
EP 1 262 373 describes a back-lit electroluminescent license plate arrangement that also provides retroreflectivity. A further back-lit electroluminescent license plate is disclosed in WO 04/048155.
EP 1 477 368 discloses an illuminated license plate for vehicles, comprising a light guide having opposite major front and back faces and side faces there between, an elongate light source arranged along at least a portion of at least one of the side faces of the light guide for illuminating the light guide, a light-transmissive retro-reflective film, and indicia, wherein the light-transmissive retro-reflective film and indicia are arranged in front of the front face of the light guide. According to a particular embodiment, it is disclosed that the illuminated license plate is encapsulated by a frame and held against a back plate.
It has now been found that in an arrangement as disclosed above where the light guide is held in a housing against a back plate, damage may occur to the light guide and/or light sources, for example LEDs that are arranged on the side faces of the light guide to illuminate the latter. In particular, it was found that this damage may occur over time when the license plate is in use on a car as a result of vibrations occurring in the license plate assembly. It was found that these vibrations occur as a result of manufacturing tolerance of the light guide that need to be accommodated when assembling the license plate and light guide in a housing.
It would now be desirable to overcome one or more of the aforementioned disadvantages.